The invention relates to a piston securing device for a cartridge, in particular for a multicomponent cartridge, which is suitable for the simultaneous dispensing of a filler material. In the case of a multicomponent cartridge, the filler material is comprised of at least two components. The discharge of the two components takes place separately. The two components can only be mixed directly before use to be supplied to their intended use as a mixture.
Such a multicomponent cartridge is already known from WO9105731. This multicomponent cartridge includes a first hollow space and a second hollow space which can each be filled with a respective component. The first hollow space and the second hollow space have the shape of a cylinder and are arranged next to one another. Each of the two hollow spaces opens into a discharge nozzle through which a respective one of the components is discharged. A static mixer can be connected to the two discharge nozzles and the components being discharged separately through the discharge nozzles can be mixed with one another in it. Instead of the static mixer, a closure element can be connected to the discharge nozzles which serves for the closing of the two openings formed by the discharge nozzles. This closure element is required to store the two components separately in the first and second hollow spaces and to shield them from environmental influences such as light, atmosphere and the like.
A seal can be applied to the filling end of the first and second hollow spaces disposed opposite the discharge nozzles and likewise serves the purpose of storing the two components separately in the first and second hollow spaces. This seal is attached to the filling end subsequent to the filling of the first and second hollow spaces with the corresponding component. The filling of each of the two hollow spaces thus takes place at the filling end of the multicomponent cartridge. This seal is formed by a piston which is movable in the storage chamber.
It is disadvantageous in this structure that the piston inserted into the storage chamber after the filling is not fixed in the inner wall and it is thus possible that the piston is pressed at least partly out of the storage chamber, whereby it can lose its sealing function. The filler material can then be discharged in an uncontrolled manner, which makes the cartridge unusable and damage can arise due to corrosive or toxic filler materials. Such a movable piston also reacts actively to environmental influences such as an expansion of the fluid filler materials due to temperature fluctuations. The piston is urged in the direction of the filling end of the cartridge by the pressure forces hereby resulting and there is the risk of a displacement from the cartridge and of the uncontrollable discharge of filler material.
The securing of the piston previously took place by means of a cap which closes the cartridge base in a substantially form-fitted manner. However, this solution requires an additional component which allows the form-fitted connection of the cartridge and the cap. This means that an additional part has to be produced in the production process and has to be mounted onto the cartridge after the filling process. The additional part causes additional manufacturing costs. In addition, the filling of the cartridge is in many cases not carried out at the location at which the cartridge is manufactured. This has the consequence that the logistical effort is increased by this additional component, which makes this solution appear undesirable for economic reasons.
There is also the solution of providing a piston retention groove at the inner wall of the cartridge. This piston retention groove can, however, only be used for a specific dimension; otherwise the piston cannot be held in the piston retention groove. This dimension is in particular the inner diameter of the cartridge which amounts to at least 20 mm.
A further solution is the provision of a retention means, which is formed at the inner wall of the cylinder delimiting the storage chamber of a multicomponent cartridge, as shown in EP0688727 A1. The retention means consists of two retention elements which are arranged at an angle of 180° at the periphery of the inner wall. This retention means has to be assembled in a separate working step after the piston has received its final position in the cylinder, the cartridge being thus completely filled. Thus an additional working step and a special tool are required. By means of this special tool a portion of the cylinder wall is cut through and the cut through portion is flapped as a retention flap into the inner space. The piston rests on this retention flap and is supported thereby in a safe manner against loss. The cutting through and flapping of the retention flap is obtained according to EP 0688727 A1 by a pressing. For performing this operation it is necessary to stiffen the cylinder locally by a stiffening ring, such that it does not loose its shape during the pressing operation and filler mass may be discharged due to a leak appearing between the piston and the inner wall by the deformation of the cylinder wall. This process is complicated and due to the additional manufacturing step expensive.
Thus it is proposed according to EP0351441 A1 to foresee protrusions at the inner wall of the cylinder of the cartridge. However the piston has to be sufficiently flexible, so as to pass these pre-manufactured protrusions without damage, which entails additional requirements for the piston. It is also suggested that the cartridge body itself can be configured to be flexible which however can entail the above-mentioned problem of possible leakage of filler mass, if the piston passes the prefabricated protrusions and the cartridge body is deformed such that the piston looses contact to the wall.
A further solution has been proposed in DE202004017878 U1, according to which a lip is foreseen on the outer body of the piston, which engages in a groove at the cylinder wall. The lip engages in the groove such that the piston is fixed into its position. That means, that with this solution the piston can not be displaced into the direction of the discharge opening, when he is snapped in. Accordingly a complete filling of the cartridge after the setting of the piston is impossible. An air cushion remains between the filling mass which is pressed through the discharge opening into the inner space of the cylinder and the fixed piston. During the filling procedure, the air cushion is compressed and has to discharge either through a ventilation valve arranged on the piston or bypassing the filling mass through the discharge opening. Both solutions can have the consequence that air remains enclosed between the piston and the filling mass and the cylinder is filled incompletely.